The invention relates to an electrode-inlead assembly for electrical lamps which comprises a lead-in-wire, a foil made of refractory metal and an electrode with a shank made of refractory metal, wherein one end portion of the lead-in-wire is welded to one end portion of the foil. Furthermore, the shank supports the electrode on its one end portion, while the opposite end portion of the shank is welded to the opposite end portion of the foil.
The present electrode-inlead assembly can be utilized with several kinds of electrical lamps, most favorably with the double-ended lamps, for example, double-ended metal halide lamps or incandescent lamps in a quartz vessel, etc.
The electrode-inlead assembly mentioned in the introductory paragraph is well-known and discussed for example in the U.S. Pat. No. 4,968,916.
Usually, some technical problems arise at the manufacturing of the mentioned electrode-inlead assembly.
One problem is that in some cases of higher precision requirements, e.g. with metal halide lamps, the electrode tips can not be located accurately enough in the centerline of the lamp. Namely, this construction has the electrode offset from the centerline of the foil. Since the foil width fills the middle of the tubular end portion of the quartz vessel during the manufacturing, the foil is located in the centerline of the lamp and the shank of the electrode is welded on the foil, thus the electrode will be displaced from the centerline of the lamp by half a shank diameter (a further displacement caused by the foil thickness can be neglected).
Another problem is that the welding of refractory metals like the materials of the shank and the foil can be accomplished only with difficulty. Usually, it is necessary to add some brazing material to the welding, such as a platinum tab, in order to make the welding easier and the bond between the shank and the foil stronger.
A further problem can arise in case of lamps of higher current operation, where a larger shank diameter is required for achieving a higher thermal mass and conductivity. A very large shank diameter is difficult to weld to the foil and to shrink the quartz material of the lamp vessel surrounding the seal, even with the utilization of an extra seal coil on the shank for the reason of preventing the cracking of the quartz, which is also covered by the U.S. Pat. No. 4,968,916 mentioned.
The present invention provides an electrode-inlead assembly which eliminates the problems mentioned.